1. Field of the Invention
The present invention relates to a white balance adjustment circuit and an image-capturing apparatus that includes the white balance adjustment circuit.
2. Description of the Related Art
In an electronic camera that captures a subject image having passed through a photographic lens by using an image-capturing element such as a CCD image sensor, a white balance adjustment is executed in order to achieve a predetermined ratio among the signal levels of image-capturing signals corresponding to R, G and B colors obtained from the CCD image sensor. Under normal circumstances, the gain to be applied to the R color signals and the gain to be applied to the B color signals are determined relative to the G color signal gain in the white balance adjustment. Japanese Laid Open Patent Publication No. H 11-341500 (hereafter referred to as reference literature 1) discloses an image-capturing apparatus that executes a white balance correction (coarse adjustment which will be described below) together with the white balance adjustment described above when there is a change in a photographing condition. In this image-capturing apparatus, the white balance is corrected in conformance to whether or not an ND filter is currently inserted between the photographic lens and the image-capturing element.
The image-capturing apparatus disclosed in reference literature 1 corrects (coarse adjustment) the G color signal gain in conformance to whether or not the ND filter is currently inserted and the gains for the R color signals and the B color signals are determined (finely adjusted) relative to the corrected G color signal gain. Generally speaking, the G color signals are often utilized to obtain brightness information in exposure calculation and, for this reason, there is the risk of the exposure becoming changed if the G color signal gain is adjusted.